I need to find the largest and smallest value for f(x,y) in a particular domain.

$\displaystyle f(x,y)=x^2+x(y^2-1)$ and $\displaystyle x^2+y^2\leq17$

I found the stationary points but I have trouble when I insert the domain in f(x,y) $\displaystyle g(x)=x(x+16-x^2)$ as the answer I get is not right.

How would you solve the problem?

Thanks